Thermal Inactivation Kinetics of Horseradish Peroxidase

Thermal inactivation of horse radish peroxidase (HRP) in buffer and sucrose solution was studied with Differential Scanning Calorimetry (DSC) and by determining residual activity. For both experimental systems, the apparent reaction order for thermal inactivation was 1.5. Since the four isozymes varied in heat‐resistance, the 1.5 order was probably due to heterogeneity of HRP. An increase in the maximum denaturation temperature by DSC as sucrose concentration increased suggested that the addition of sucrose stabilized the enzyme against thermal denaturation. However, based on the determination of residual activity, sucrose reduce thermal stability of HRP at 10–20% (w/w) and increased thermal stability when the concentration was 40% or greater. At equimolar concentrations of fructose, glucose or lactose at 90°C, HRP was more rapidly inactivated than in the presence of sucrose.